There is a case where the surface of oxide glass such as soda lime glass, synthetic quartz glass, phosphate glass, borosilicate glass or alkali-free glass is desired to be treated for fluorination. For example, there is a case where the surface of such oxide glass is desired to be treated for fluorination to impart an anti-fouling property, hydrophilicity, adhesive property, moisture-proof property, anti-reflection performance, etc. to the surface of such oxide glass. In this specification, “the surface of oxide glass is treated for fluorination” means a treatment to introduce fluorine to a portion in a certain depth from the surface of oxide glass, for example, to a portion in a depth of about 2,000 nm from the surface (hereinafter, referred to as “the surface layer”).
As a method for treating the surface of oxide glass for fluorination, a method is known to fix or dope fluorine on the oxide glass surface by a chemical vapor deposition (CVD) method, a physical vapor deposition (PVD) method, a gas deposition method or the like (Patent Document 1, Patent Document 2).
However, such a method utilizes a vapor deposition method, whereby there is a problem such that the adhesion of fluorine to the oxide glass is poor.
Further, the material which can be vapor-deposited is rather limited, and an expensive material is obliged to be used, whereby the production cost tends to be high.
Further, Patent Document 3 discloses a technique of adsorbing fluorine on the surface of a glass substrate in a method for producing an electron emission element. However, in Patent Document 3, the procedure of adsorbing fluorine on the surface of a glass substrate is carried out under a condition of a low reaction rate under a very low pressure at a level of 1.3×10−2 Pa, whereby it takes time for the fluorination treatment, and in addition, as the purpose of Patent Document 3 is to adsorb fluorine on the surface of a glass substrate, the condition is considered to be such that no fluorination reaction will proceed between fluorine and the glass substrate surface or a fluorination reaction proceed only at the outermost surface of the glass substrate. Accordingly, the fluorine atom and the glass substrate have no chemical bond, or even if the fluorine atom and the glass substrate have a chemical bond, such a bond is only at the outermost surface of the glass substrate, whereby there is a problem such that the intended effects cannot sufficiently be obtained, or the intended effect cannot be maintained for a long period of time for such a reason that the adsorbed fluorine is likely to be easily eliminated.
Patent Document 1: JP-A-2002-539066
Patent Document 2: JP-A-2001-253729
Patent Document 3: JP-A-2000-21300